The present invention relates generally to storage media and more particularly to storage media that utilizes depressions and/or raised features.
Data storage on a rotating storage media requires position sensing information to be included on a part of the media surface so that a data can be accurately accessed using the media. Prior art devices have traditionally used different methods to encode and store this position sensing information.
Traditional Winchester magnetic storage systems use magnetic signals recorded in the thin film media surface for this purpose. The position sensing information is typically recorded by the same systems used to write data to that surface in a process known as servo writing. The position sensing information is recorded on the media by an external servo writer to provide track identification and position, which is then used during the writing and reading process to accurately position a flying head during these operations. Typically the data is arranged in a concentric series of tracks, each track being made up of a number of sectors, which each in turn contain multiple bits of binary data. Since the position sensing information is recorded on each recording surface of the storage media one disk at a time, the time required to complete the servo writing process increases as the total number of disks, sectors and tracks increases.
In optical data storage systems using optical disks, for example, CDs and the like, diffraction information obtained from light reflected from disks may be used to provide the position sensing information.
In other optical data storage systems embossing processes may be used. Here the servo sector information maybe written using optical lithographic systems. A series of pits may formed and replicated onto a surface of a metal mold. Numerous plastic disks with accurate copies of this pattern may be produced by injection molding processes. Since the molding operation is fast and low-cost, the complete servo information is provided on the entire disk surface with this inexpensive process, making writing of individual sector information on the disk unnecessary.
In such optical systems the pits are typically required to have very tight dimensional tolerances to perform adequately in their intended use. For example, the depth of the pits should be controlled to a specific fraction of the wavelength of light used, for example, xc2xc wavelength of 650 nm light. The observed servo signal is caused by destructive interference that occurs between light reflected off the pits, so that changes in the pit depth result in changes in the magnitude of the reflected optical signal. Since interference is used to generate the signal, significant lateral changes in the size of the spot can cause the adjacent pit edges to effectively overlap, reducing the magnitude and distorting the shape of the servo signal. Thus, accumulation of contaminants in the pits can act to reduce the amplitude of the reflected signal. Also, the presence of pits can act to reduce the smoothness of the disk and thus can cause head flyability problems for heads that are intended to fly near the surface of the media surface.
Magnetic and optical technologies can be combined whereby the optics are used to transmit light to provide thermally assisted recording and reading of data on a storage disk. In this type of magnetic-optical system pits may also be provided for servo tracking in the manner described above. However, the application of the light to the storage disk can cause undesired heating effects in the storage disk.
What is needed, therefore, is a method and apparatus that acts to reduce the undesired effects of pits and heating in a magnetic-storage drive of the prior art.
The present invention provides for the enhancement of the storage capacity of a data disk drive while reducing optical path optics, electronics and/or the mass and complexity of associated read/write heads. The system utilizes light transmitted by optical elements to servo track a data disk and to heat the data disk during writing and reading of data, and inductive and magnetic elements for actual writing and reading.
The data storage disk may include depressions and/or raised features, which may be filled and/or polished with various materials. In this way, a smooth surface is provided for the read/write head that is aerodynamically maintained in a flying condition very close to the data disk surface. By providing a smooth surface, accumulation of contaminants may be reduced or eliminated. The filler material may be made to be reflective such that an optical signal reflected from the depressions and/or raised features can be provided with a larger amplitude. The reflection of the light from the material used for filling the depression and/or raised feature may be used for sector identification and track following. Additionally, the depressions and/or raised features may be made to present a reflective area that is proportional to the radius of the data disk at which they are disposed. Consequently, the frequency content and/or amplitude variations of the reflected optical signal may be minimized over a radius of the data disk.
In the present invention, the data storage disk may further comprise a set of channels and/or mesas disposed in-between data tracks comprising the data storage disk. The channels and/or mesas may be used to thermally channel and direct the thermal effects of the light applied to the data disk such that the shape of data domain marks that are used to store data along the data tracks may be confined in a cross track direction and defined to more accurately match a preferred rectangular or square geometry. The storage density and SNR may consequently be increased. The channels and/or mesas may be also be filled with a filler material.
One element of this invention is the use of a differential removal process such as chemical mechanical polishing C. M. P., which is a process primarily used in the integrated circuit industry to control planarity of deposited and patterned layers. The deposited layers used to form insulating and conductive regions in the integrated circuits are generally conformal, in the sense that their as-deposited thickness is constant regardless of the topology of the underlying regions.
As multiple layers are deposited, patterned and etched, it becomes increasingly difficult to correctly perform the lithographic steps of surfaces that are no longer smooth and flat. In the present invention, polishing steps are incorporated after deposition steps to return a disk surface to being flat and smooth, after which the record lithographic steps can be performed with sufficient accuracy. Both equipment and processes have been developed to polish various layers in the presence of other layers such that there is a large selectivity on the removal rate between different layers. The layers with the lower polishing rate for so-called etch stops (actually polish stops), which prevent further polishing after the lower polishing rate material is exposed.
The invention includes the formation of a master pattern of depressions or raised features and the subsequent transfer of that pattern to a disk substrate. On top of that substrate, at least one sacrificial layer is provided atop a relatively hard layer. By sacrificial layer it is meant that the layer is relatively easy to etch or otherwise remove in a controlled, planar step. By a hard layer, it is meant that the layer is relatively polish or etch resistant. A data storage layer may serve as this hard layer.
For example, in a magneto optical design, the recording stack may be provided with both silicon nitride and silicon dioxide top layers, with the silicon dioxide layer acting as a sacrificial layer to ensure that the hard layer, of silicon nitride, remains at the end of the process. In a further alternative, a layer of aluminum or aluminum alloy may be deposited, with the aluminum plugs filling the depressions or raised features (created by the embossed servo information) to a level higher than any of the adjacent layers of silicon dioxide, silicon nitride, or similar that dielectric layer. Since the polishing rate of the aluminum can be far faster than that of the silicon dioxide, then the aluminum can be etched or otherwise removed down to a level equal to or slightly below a planar surface with the silicon dioxide, with the silicon dioxide layer allowing for some small level of over polishing. Thus, the silicon nitride layer is preferably protected; the silicon dioxide layer partially remains and is partially removed; and the aluminum metal which fills the pits rises only to a level substantially equal the very flat top surface of the silicon dioxide.
Alternative filler materials may be used in a similar process as long as an appropriate selective removal process is available with sufficient selectivity. In this example, the aluminum functions as a sacrificial layer; the silicon back side is effectively served as a hard layer, and it is removed more slowly. In an alternative embodiment, the silicon dioxide layer could be omitted, with the silicon nitride layer now being the hard layer. For conventional magnetic recording disks, the depressions or raised features may be filled with a non-magnetic material such as aluminum, glass or polymer, such as polyamide, or a magnetic material of higher or lower permeability, coercivity, or susceptibility and polished smooth. Such fill material again is selected on the basis of its removable selectivity relative to the basic hard material of the magnetic recording disk.
The present invention may comprise a storage disk, the storage disk comprising a substrate, the substrate comprising a top surface and a bottom surface, the top surface and the bottom surface defined by raised surface portions and depressed surface portions, the raised surface portions of the top surface and the raised surface portions of the bottom surface disposed along planes that are substantially in parallel opposition to each, and the depressed surface portions disposed between the planes; at least one layered first material, the at least one layered first material comprising a top surface and a bottom surface, the bottom surface of the at least one layered first material disposed above the raised surface portions and above the depressed surface portions, and the top surface of the at least one layered first material disposed to extend above the raised surface portions and above the depressed surface portions; a layered second material; the layered second material comprising a top surface and a bottom surface, the bottom surface of the layered second material disposed above the top surface of the at least one layered first material and above the depressed surface portions, and the top surface of the layered second material disposed above the raised surface portions and above the depressed surface portions; and a layered third material, the layered third material comprising a top surface and a bottom surface, the bottom surface of the layered third material disposed above the top surface of the layered second material and above the depressed surface portions, and the top surface of the layered third material disposed at a level of the top surface of the layered second material. The layered third material may comprise a metal material, a polymer material, or transparent material. In the present invention the storage disk preferably comprises a topmost surface and a bottom most surface, wherein the topmost surface and bottommost surface are substantially flat over their entire surfaces. The at least one layered first material may comprise a storage layer and a readout layer. The at least one layered first material may comprise a magnetic material. The raised surface portions and the depressed surface portions may comprise a servo pattern. The storage disk may comprise a plurality of data tracks, wherein the raised features comprise mesas or channels, and wherein the mesas or channels are disposed between the plurality data tracks.
The present invention may comprise a disk drive, including a disk substrate, the disk substrate comprising a surface, the surface comprising raised features and depressed features, the raised features comprising a topmost level; and a filler material, wherein the filler material is disposed in the depressed features to a level substantially equal to the topmost level of the raised features. The disk drive may further comprise a source of light, wherein the light is directed along an optical path between the source and the disk substrate based on a reflection of the light from the substrate. The raised and depressed features may comprise a servo pattern, wherein the light is reflected from the servo pattern. The disk drive may further comprise a storage layer and a source of light, wherein the light is directed along an optical path between the source and the disk substrate to heat the storage layer.
The present invention may comprise a storage disk, including a disk substrate, the disk substrate comprising a surface, the surface comprising a plurality of servo features, the servo features comprising a dimension that is proportional to a radius of the disk substrate at which the servo features are disposed.
The present invention may comprise a method of utilizing a storage disk that comprises raised and depressed features, including the steps of defining the raised and depressed features in a substrate; depositing an etch stop layer over a surface of the substrate comprising the raised features and the depressed features; depositing a filler material over the etch stop layer to a depth sufficient that the depressed feature is filled to a height substantially equal or above the etch stop layer; and differentially removing the filler material so that the filler material over the etch stop layer is removed with little or no removal of the etch stop layer to leave a substantially planar surface comprising the filler material and the etch stop layer. The method may further include the step of depositing a sacrificial layer over the etch stop layer and before depositing the filler material layer; and wherein the etching step substantially etches the filler and the sacrificial layer to leave a substantially planar surface comprising the etch stop layer and the filler material. The etch stop layer may comprise silicon nitride and wherein the sacrificial layer comprises silicon dioxide.
The present invention may comprise a storage disk, including a disk substrate, the disk substrate comprising a surface, the surface comprising raised features and depressed features, the raised features comprising a topmost level; and disk substrate leveling means for leveling the depressed features to a level substantially equal to a topmost level of the raised features.
Other features and advantages of the present invention will become apparent to person of skilled in the art who studies the following invention disclosure. The present invention is not be limited to the specific embodiments disclosed in this application or any equivalent thereof, as the invention, as described, may be used in any of a number ways, known and unknown at this period of time.